Effects of temperature, humidity, air pressure?

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johnwoitalla

johnwoitalla

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Jul 23, 2021
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California, United States
Do any of you keep records on Air temp, humidity, and/or air pressure when you shoot targets for accuracy? I shot my RWS 54 today at the range. It was foggy and about 55°F. The POI was about 0.5” higher at 25 yds than the last time I went when it was much warmer and dryer. When I went in July, the JSB’s shot at about 1” at 25yds, same gun and distance in cooler dry air the JSB’s shot about 0.65” at 25 yards all were in the bullseye with 10 shots. The difference in air temp between today and in July was about 40°F. I have strong suspicion the these factors play a greater roll in the performance of my shooting than I had previously accounted for. I haven’t been able to shoot my PCP yet, but I’m guessing I will see much of the same influences upon group sizes and POI with it as well. What are your experiences with these factors with respect to your results?
 
Keep in mind that hot air compresses differently than cold air, also keep in mind that dry air is not as dense as humid air. With that in mind, when the air changes so will your impact point as the air will compress differently. Heat allows for expansion where cold temps usually contract. All these things must be taken into consideration when shooting for accuracy. 
 
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In a spring piston rifle I would think colder temperatures could affect the seal and tar depending on type and amount used. I don't know if going from 55* to 40* would cause this. The piston seal might contract enough to reduce surface contact in the chamber. Or the breech seal might also be affected. I haven't used my current springers in colder temps, but will start looking into temps and accuracy since one has a leather seal. Temperature during storage and transport might also play a part. 
 
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Your thinking is correct but dont get carried away....the changes are very small, most notable on long shots, very little change on close shots. I never liked the tar myself, always used Dow111 silicone grease as it is affected less by cold and heat. First few shots are most affected, the cylinder does warm up a little after a number of shots. I found a 10-20 degree temp change doenst cause much change but a 25-40 degree change can be noticible. Take notes at different temps and keep a log so corrections can easily be made. Thats what I do...
 
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I've noticed that gas rams are definitely affected by cold. Spring power not as drastic.
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Ya, i see that . I had pics of a test i did here as the morning temp was say 55' and it quickly warm d up to like 75'. Also like barometric pressure on the ram air/gas.

It was a pretty good swimg in poi.

If advertised as used i thought "inert" gas used should not be affected by this like normal "air" is. Hmmmm. I got to wonder what if any inert gas is even used as claimed by some.

https://hardairmagazine.com/reviews/do-gas-ram-air-rifles-give-different-fps-at-different-temperatures/




 
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As mentioned, elevation plays a big role in effects on velocity for springer airguns. I saw a 12 fps loss going from 85 ft to 1000 ft of elevation using my .22cal RWS 34. I had a 5mm Beeman RX1 that lost 25 fps going 85 ft to 2400 ft. Chronograph verified! 

Gas spring airguns are effected by temperature to some degree. The Sig ASP20 that I use to own would lose close to 20 fps going from receiver tube temperature of 80-85 degrees to 50-60 degrees. Again, chronograph verified! Temperature doesn't seem to have much of an effect on spring piston airguns from my tests.
 
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If you refer to the General Gas Law, you will find this to be true. Temperature and pressure are directly proportional, as temp rises, pressure will also rise, and vice versa (given that volume doesn't change).

Volume and pressure are indirectly proportional, as volume is reduced, pressure will increase, (given temperature doesnt change)

Gas rams are sensitive to temp changes much more than coiled spring power plants, what is sensitive to temp changes in a spring gun is the lubricants depending on what type and how much lube is in the gun. Cold temps will cause the lubes to stiffen somewhat. If it is cold outside and I'm shooting my HW80, I let it warm up in the sun a little to make sure the lubes are not stiff before shooting. Keeps everything consistant.

Humidity and baro pressure have much less affect than temp and pressure.



-Eric
 
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I shoot my three TX200s in weather from 90 degrees plus down to about 20 degrees in winter. The gun pretty much shoots the same and I lube very sparingly with Krytox. The Premier Leupold I have ranges very well through the whole range, but the Sightron changes for hot and cold temperatures. As long as I compensate for the range difference, the gun does its part.
 
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AirShot said:
Keep in mind that hot air compresses differently than cold air, also keep in mind that dry air is not as dense as humid air. With that in mind, when the air changes so will your impact point as the air will compress differently. Heat allows for expansion where cold temps usually contract. All these things must be taken into consideration when shooting for ry air is actually denser than humid air.
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AirShot said:
Keep in mind that hot air compresses differently than cold air, also keep in mind that dry air is not as dense as humid air. With that in mind, when the air changes so will your impact point as the air will compress differently. Heat allows for expansion where cold temps usually contract. All these things must be taken into consideration when shooting for accuracy.
Click to expand...
Dry air is actually more dense than moist air at the same temperature.
 
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TonvanderLinden said:
Dry air is actually more dense than moist air at the same temperature.
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Could be, just going by what the weatherman keeps telling us. My friend is a pilot and claims his aircraft goes faster in dry air due to less density...but I am not a pilot so only going by what has been told to me over many years. Probably global warming changed everything...lol....
 
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